Fertilizer production helps feed nearly half the world, but it consumes huge amounts of energy and creates carbon dioxide. This study turns waste gases and wastewater into fertilizer inside a space far smaller than a human hair is wide. Urea remains the cornerstone nitrogen fertilizer sustaining nearly half of the world’s population, so its production affects food supplies on a global scale.

However, current urea production accounts for two percent of global energy consumption and one point five percent of total carbon dioxide emissions. Electrosynthesis with carbon dioxide and nitrate offers a carbon-neutral alternative that could transform pollutants into useful chemicals under ordinary conditions and make fertilizer directly from wastewater and flue gas.

The difficulty is that the carbon and nitrogen ingredients do not arrive at the reaction surface in step, so they often fail to meet and join together efficiently. Open surfaces let these short-lived ingredients drift away or enter competing reactions before they can form urea.

Earlier enclosed designs helped retain them, but their sites and spaces were uneven. The central challenge was to combine a precisely defined reaction site with a cavity whose size could regulate ingredient generation, gathering, and coupling.

The researchers addressed this like fitting a busy kitchen with a perfectly sized counter: heat was used to carve controlled cavities around isolated copper reaction sites, rather than leaving the surface completely open. The size-matched space was proposed to lower the energy barrier for molecules held inside and suppress side reactions during the reaction.

A design measure linked cavity shape with the local electric field and electronic behavior, establishing a general design principle for nanoconfined electrocatalysis. The tiny cavity stabilizes the carbon- and nitrogen-bearing ingredients needed for the joining step, while suppressing competing reactions and lowering the barrier to carbon–nitrogen coupling.

That design produced urea with ninety-eight point nine percent of the electrical reaction going toward urea in the gas-diffusion cell. The cavity size mattered sharply: the one-point-five-nanometer cavity sent the largest fraction of converted nitrate toward urea, while smaller or larger cavities favored different unwanted products.

The results also changed when the supply of either starting material was too low or too high, shifting the reaction toward separate carbon or nitrogen products instead of urea. The key carbon ingredient was carbon monoxide, while several nitrogen-containing ingredients took part in the joining process.

When nitrogen gas or ammonium was supplied alone, no urea appeared. The comparison made the role of the cavity clear: a similar copper reaction site without confinement reached only about sixty-one percent selectivity, while the confined catalyst produced a much higher urea yield.

The controls showed that the surrounding cavity enriches and retains carbon- and nitrogen-containing ingredients, helping them couple into urea. The approach was then tested with industrial flue gas and nitrate-rich wastewater in a pilot system, where it operated continuously for three hundred hours and maintained ninety percent selectivity for urea.

After operation, the material largely kept its shape and its isolated copper sites, with no obvious copper loss or clumping. In the laboratory, the catalyst reached ninety-eight point nine percent selectivity; at pilot scale, it reached ninety percent while running continuously on flue gas and nitrate-containing wastewater.

The lower pilot performance likely reflected changing feed composition, impurities, and less even movement of materials through the system, so broader testing is still needed. Although this strategy requires further validation, the analysis supports its potential for producing urea from carbon dioxide and nitrate-containing waste streams.

The key is not simply finding a better reaction surface, but building the right tiny room around it. That room keeps the needed ingredients together long enough to make urea, with strong selectivity even in a pilot system.